A "content type" is what I like to use. It can be the basic types that exist today in core (a page, a blog entry), or types that are created by specialized modules (e.g. an image, an event), or what site owners create using CCK. A "content item" is an instance of content type (for the OO heads among us). Content item should be a better name for what we call "node" today. Post can also be used, but not every item is posted to the site. For example aggregator and friends create items from other sites.